This invention relates generally to the art of making corrosion resistant valves, and more particularly, to a method of making a knife gate corrosion resistant valve.
The desirability of specially constructing corrosion resistant valves has long been recognized where valves are to be used for such things as highly active chemicals, acids, bases, solvents, gasoline and the like. A difficulty encountered in constructing such valves is that materials which are resistant to corrosion are often expensive and/or weak so that it is normally difficult and expensive to construct valve members out of such materials. One common practice in constructing corrosion resistant valves is to employ inexpensive frames or housings which have corrosion resistant linings covering those surfaces to be contacted by corrosive fluid materials.
For example, U.S. Pat. No. 3,545,480, describes a rather popular valve in which corrosion-resistant, sheet metal liners are first constructed and then a cast valve body is machined to fit the liner. A valve seat is then attached to the liner at the throat of the valve. The liner described in this patent is constructed in sections and is then assembled. It is easy to see that this construction, although saving money by not using expensive materials for the body is still unduly expensive because of the time necessary for machining parts, assembling the liner members and attaching the valve seat. Further, this valve only works in one direction inasmuch as it only has a valve seat on one side of the gate. Still further, a problem with this valve is that, since the liner is constructed of elements which must be assembled, cracks are left between the liner elements which must be filled by welding or with plastics. Thus, it is an object of this invention to provide a method for making a corrosion resistant valve in which a liner is to be made of only one piece and in which the liner is combined with a body without undue amount of work to adapt these two members to fit one another. It is also an object of this invention to provide such a method of making such a valve which produces a valve which can be used to cut off flow in either direction. Still further, it is an object of this invention to provide a method of making a valve in which a valve seat is produced simultaneously with producing the liner.
It has been suggested to use fluorocarbon resin liners for valves, and other conduit, bodies. Such suggestions are made in U.S. Pat. Nos. 3,206,530 to Boteler, 3,438,388 to Schenck and 3,026,899 to Mischanski. In each of these cases, the liner is intended to protect a body, or housing, from corrosive liquids passing through the valve body. Boteler (U.S. Pat. No. 3,206,530) mentions that the liner can be molded in the valve body housing or separately therefrom. Schenck (U.S. Pat. No. 3,438,388) heats a tube of fluorocarbon resin which he then pressurizes against the walls of a valve body using a pressurized gas. In these cases valving elements are combined with gaskets, valving-element liners and the like at the interface between the valving element and its seat. It is an object of this invention to provide a method of forming a corrosion-resistant valve in which a liner can be constructed to closely interface with a valving element in one step so that no gaskets, seats, valving-element liners or other sealing members are necessary in order to control flow through a valve flow passage. It is also an object of this invention to provide a method for making a corrosion resistant valve which works in two directions in one step.
It is yet a further object of this invention to provide a method of making a corrosion-resistant valve which is extremely inexpensive since it does not require undue machining of parts, but yet which provides excellent operation characteristics and an unusual amount of durability.